Thermally activated coal gangue regulates low-temperature pyrolysis humification of corn straw through distinct mineral-component functions

Mineral additives can regulate biomass humification during low temperature pyrolysis, but component specific effects remain difficult to distinguish. This study investigated how reconstructed mineral phases in thermally activated coal gangue (NCG) regulate corn straw (CS) humification. Metakaolin (MK), MK + Fe₂O₃, and MK + Fe₃O₄ models distinguished the contributions of aluminosilicates and iron phases. At 250 ℃ and CS: NCG = 1: 0.75, humic acid (HA) yield reached 52.90%, versus 40.70% with untreated coal gangue. Thermogravimetric and derivative thermogravimetric analysis (TG-DTG) revealed altered thermal decomposition. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed distinct polysaccharide, aromatic, and carbonyl responses. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed distinct changes in HA molecular composition. MK promoted molecular growth and unsaturation, whereas Fe₂O₃ limited highly condensed components. Fe₃O₄ favored aromatic retention and associations among oxygen-containing fragments. Full factorial analysis supported positive mineral interactions in HA formation. Density functional theory (DFT) indicated complementary interfacial roles in precursor binding and carbonyl polarization. These findings clarify how reconstructed mineral phases jointly regulate HA formation and molecular composition during low temperature humification. Economic analysis showed a profit of CNY 2866.25 t^-1 and an equivalent CO₂ reduction of 71.39 kg CO₂ t^-1. Together, these results demonstrate the practical potential of NCG-assisted humification for HA production and biomass valorization. These findings reveal component-specific regulation of HA molecular composition by reconstructed mineral components in NCG. They also clarify the mechanisms supporting synergistic valorization of coal gangue and agricultural waste biomass.